In episode 5, Thea gives one statement that shows how much she truly loves her brother "I can't lose you again."
Oliver and Thea teasing their mother in "Legacies", mostly because of the fluid chemistry; it's a rare moment where they act like normal siblings without baggage.
At the end of Legacies when Oliver and his mom share burgers at the burger joint (Moira even eats with her hands, despite her usual stuffiness). Despite the fact that he's keeping secrets and some of her more questionable actions, they're still family and they still love each other.
Also, from Legacies, Tommy gives Thea a ride home after a night of heavy drinking. Clearly ashamed of what she did, Thea begs Tommy not to hate her and Tommy replies he could never hate her.
The end of episode 8, when Tommy asks Oliver for a job, outright rejects taking any of his trust fund, and Ollie giving Tommy the job. It shows that they both care about the other much more than assumed, and Oliver is willing to help Tommy change, even if it means losing Laurel. Overall, their entire relationship can be considered this since, when first introduced, many assumed Tommy to be a shallow wingman of Oliver's.
Diggle in general being caring enough to be both an ear for Ollie to confide in as well as a voice to temper Ollie's actions. But particularly giving Ollie props for taking the risk in opening up to Helena after previously chewing him out on that particular subject (and before that, pushing him to confide in more people).
Diggle: The Oliver I met a few months ago wouldn't have been able to do that.
A small one in Ollie including Walter in his 'reason to hold the Queen Christmas party' speech. For Ollie, it's a nice gesture to show Walter that he considers him a part of the family. For Walter, it must be nice to hear Ollie say as such considering from Ollie's perspective, he came home to a different family.
The way Oliver acts about his sister Thea in Vertigo. Big Brother Instinct at its finest. Particular mention goes to the scene where they walk to the court house and news reporters start swarming in on her. She holds her hand out to him and he holds it, and then muscles his way past the mob while protecting her.
Felicity's statement to Ollie in the restaurant when she realizes the book Walter had is big news: "You've dropped some fairly ridiculous lies on me, and yet ... I still feel like I can trust you."
In episode 16, when MalcolmMerlyn realizes people are attacking the first thing he does is look for his son. He treats Tommy like crap, takes glee in tearing him down, but at the end of the day, he loves Tommy, and was even willing to reveal he's the Dark Archer to him. In the end, the two have a heart to heart, and almost explains his backstory.
Same episode, when Moira, who hired the hit on Malcolm, sees Tommy in the crowd and realizes that, if Malcolm dies, Tommy loses his father, and her face drops. She hates Malcolm, but she's not cold blooded enough to want to cause Tommy, her son's best friend since childhood & the nicest guy in the show, any pain at all.
Keeping with the Tommy/Dead to Rights theme, Oliver tells Tommy who he is. And while Tommy is in shock, he still covers for him when the police question him. In later episodes, after the two fall out, Tommy still covers for him, regardless of his personal feelings about him.
In "Unfinished Business", Shado is afraid that what her father, Yao Fei had to do on the island to survive turned him into a monster. Island!Ollie reassures her by saying that Yao Fei saved his life.
In Savior, Felicity can't track/fails to track a growing threat. Oliver doesn't blame her and said "Sometimes we lose." She then goes on to tell him (after noticing Oliver's tendency towards isolation), that maybe it is better off being alone, because she wouldn't know how she'd talk about what'd happened to her that day if she had a significant other in her life. After she figures out what happened with her error and the threat is neutralized. Oliver revisits the conversation.
Oliver:(quietly) Psst, by the way, if you ever need to tell someone about your day...you can tell me.
Home Invasion: After seeing how important it is to him that he finds the Vigilante, Thea tells Roy that she'll do what she can to help him find the guy.
Thea: Finding him means the world to you, and you mean the world to me, so I'm here to help.
Tommy consoling the young Taylor, who has just lost his parents, just like Tommy himself lost his mother when he was a kid, and telling him that he can see his parents every time he closes his eyes.
Roy's reason for trying to find the Hood summed up easily:
Roy: It feels like my life is connected to his.
The Undertaking: The family reunion with a rescued Walter, including Walter calling Oliver "son".
In the same scene, Ollie and Walter introducing Felicity to Moira and Thea as their friend.
Ollie's final speech to a not long for this world Tommy.
Diggle and Felicity refusing to abandon Oliver when he needs them in the finale, cementing that they are True Companions.
In that same scene, the Hood and Quentin cementing their alliance, each saying that the city needs the other.
Back in the Island time, how does Oliver gain the focus to fire his first accurate shot from a bow? When Fyers is holding Shado hostage and he's the only person still standing and able to do anything.
The Season Two opener, "City of Heroes", ends with someone coming to rescue Oliver and Queen Consolidated from a hostile takeover, someone mentioned as family after Moira's role in the Undertaking left the family without any friends. At the end of the episode, this backer walks in and it turns out to be Walter — no matter what's happened, he still considers Oliver and the company to be very close to him.
Oliver calling Felicity a good friend. It's easy to see that means a lot to her.
Moira tells Thea that being arrested and sent to jail has "freed" her from the burden that she had to do in terms of being involved with the Undertaking.
All of "Identity", Felicity is not happy with becoming Oliver's personal assistant (so that it doesn't look so odd for the CEO to go down to IT all the time); she tells him upfront that she didn't graduate from MIT just to fetch him coffee. Every single time he asks her, it's no. But at the end, Oliver's been having a rough day, so she brings him a cup, stating just this one.
Don't forget, this happens right after Oliver apologizes to Dig for not being there for him; even with Dig's joking remark that "this is getting dangerously close to hug territory", it's sweet to see them back on the same page. He even offers Ollie a ride home, though the new CEO proves to have some work to do.
Oliver: I'll find my own way.
Diggle: You always do.
Roy and Thea getting back together at the end, with him promising to stop fighting bad guys. After all, the Arrow has given him another way to help.
This other way to help, by the way, is a mix of both Oliver slowly accepting Roy and making sure Thea is happy, as relationship problems are the last thing she needs after Moira's being imprisoned and facing a death sentence.
In "Broken Dolls", Lance is wondering at Felicity's prowess with the computers while infiltrating a lab with the Arrow. That gets a smile of pride out of Ollie (under the cover of the hood)
Quentin openly thanking the Arrow for saving him and Laurel at the end.
"I might not agree with your methods, but I do agree with the results."
In "Crucible", Ollie is willing to let Quentin and Laurel hate him if it means allowing Sara to get back to her family. Also, Oliver and Sara holding hands, meaning that she will confront them.
In the same episode, Roy saves Cindy/Sin after the Mayor's attack. Thea grows to accept Roy's Chronic Hero Syndrome better, and Sin warms up to him. Meanwhile, in the hospital Sara risks exposing herself just to make sure her friend is safe.
Sebastian Blood's genuine thanks to Oliver for saving him in the Mayor's attack, attributing it to Oliver's strength as a person rather merely being instinct as Oliver insisted. Of course, it's undercut by the reveal that Brother Blood isn't as altruistic as he first appears.
A subtle one spanning over several episodes so far: both the Arrow and Felicity insist on calling Lance "Detective" in spite of his demotion, showing their respect for the guy.
In "League of Assassins", Sara reuniting with her father.
Thea and Oliver convincing Moira that whatever she's hiding, they won't stop loving her.
Oliver and Diggle sharing a bottle of vodka, probably courtesy of Anatoli Knyazev, and Ollie starting to open up more to Dig about what happened during his five years away.
Oliver insisting on confronting the Assassin Al-Owal along with Sara, because Al-Owal "threatened somebody that he cares about", ie. her.
"Keep Your Enemies Closer", after Diggle has admitted to needing to find Lyla, who was going after Deadshot:
Oliver: Felicity... I think it's time we visited our Queen Consolidated subsidiary in Moscow.
Diggle: Oliver, what are you doing?
Oliver: Just need to help a friend.
Diggle: I can't ask you to do that.
Oliver: You didn't.
Moira reconciling Roy and Thea near the end of the episode.
Shado refusing to leave Slade behind, instead staying in the plane to help him recover from his burns, with both telling the other they'd always protect ones they care about. Usually their interactions consist of snarky comments, attempts to out-badass the other, or Slade hitting on her, so its kinda nice seeing them act genuinely caring for the other.
"State vs. Queen" - honestly this episode was just full of the Heartwarming, despite it's actual plot line.
Moira is acquitted, against all odds. Sadly the heartwarming is marred when it's revealed Malcolm bribed the jury to get the verdict.
When Diggle appears to be sick, Oliver sends him home despite the fact that Oliver was going to need support as its the start of his mother's trials. When he collapses, Oliver rushes to him straight away, even though his mother's trial was still on-going for the day.
After it's revealed that Diggle's suffering a form of Vertigo withdrawal and Felicity reveals that The Count escaped the same way the Dollmaker did and the prison covered it up, Oliver looks furious and rather decisively and a little viciously grabs an arrow from his stash. Felicity starts to say "I know what you're thinking..." implying she thinks Oliver believes he should have killed the Count. Oliver replies quickly "No, you don't. I made a choice not to put an arrow in this guy... And it was the right choice.There's no more killing.'' Not only was it the explanation, but how he said it. He both lowered volume and calmed his voice to calm and bolster Felicity. And the arrow he grabbed? A possible cure for Diggle.
After that Felicity gets kidnapped by the Count and Oliver immediately rushes off to save her despite the fact that he and Thea are waiting on his mother's verdict. The True Companionship between the three has grown stronger than ever, to the point that Oliver broke his promise to never kill again when the Count tried to kill Felicity via Vertigo OD. Especially considering that the Count used that very thing to escape capture from the Arrow the first time, they encountered each other in the episode, hiding behind people and only giving Oliver room for kill shots, then when he did have a target, he revealed his hostage, whom Oliver chose to get out instead of going after the Count.
And afterwards Felicity apologizes for forcing Oliver to choose between breaking his Thou Shalt Not Killrule and letting her die. Oliver replies that as soon as her life was threatened, it wasn't a choice.
Early on, Thea is stressed out by the trial, believing she failed her mother with her testimony. Roy gets her boxing gloves and gets her to vent her anger in a weird yet cute way that proved very effective.
Barry and Felicity's interactions and these doubled on with Adorkable moments coming from the two who just radiate the stuff. Whether it's awkward flirting or just plain out the two of them nerding out, it's definitely something sweet to see.
After confronting Barry for lying to them, Felicity is upset at Oliver, because Barry had good reasons and they do the same thing everyday. At their Q.C. party, he asks her if she has time for a dance. She replies that she doesn't want to dance with him. Oliver says he knows and that's why he invited Barry. He made peace with him especially for Felicity. But they will card him at the bar.
Both the videos John Barrowman uploaded of the cast hanging out (as seen in the Funny page), especially since the actors involved (Barrowman and Colton Haynes) never interact on screen.
Stephen Amell, David Ramsey, and Emily Bett Rickards recording a video as part of the "Batkid" Make-A-Wish project (a heartwarming story in it's own right). Add to that the fact that, unlike other videos from the set which are little more than Stephen Amell goofing around with his smartphone, this was a professionally done scene, meaning that at least part of the crew also volunteered their time to record it.